Experimental measurement of atomic composition in sooting luminous flame by Laser-Induced Breakdown Spectroscopy

Abstract

In the present study, Laser-Induced Breakdown Spectroscopy (LIBS) was applied to the measurement of fuel-rich propane-air luminous flame in a counter-flow configuration to investigate the applicability of LIBS to measure local chemical composition in sooting field. H656nm/O777nm intensity ratio was chosen as the indicator of atomic number ratio H/O which gives direct information on equivalence ratio and is important for analyzing not only blue flame but also sooting flame. Measurement was conducted in the first place on propane-air/air counter-flow flame with the range of local equivalence ratio 0–4, in which the intensity ratio showed a good linear correlation with calculated H/O atomic number ratio as it had been observed in non-sooting conditions. LIBS technique was also applied to uniformly sooting flame supplying the same mixture at equivalence ratio of 2.2 from both nozzles to produce predefined homogeneous atomic composition. The measured intensity ratio was a good agreement with the linear relationship obtained in the propane-air/air diffusion flame experiment. Therefore, robustness of LIBS measurement of atomic/molecular composition in sooting flame was reasonably elucidated.